Telephone system



April 20, 1937. R. TAYLOR ET AL TELEPHONE SYSTEM 14 sheets-sheet 1 Filed April 23,y 1954 April 20, 1937. R. TAYLOR ET AL TELEPHONE SYSTEM April 20, 1937. R. TAYLOR ET ,M Y 2,077,861

TELEPHONE SYSTEM Filed April 23, 1934 14 Sheets-Sheet 5 PF /4 c5 1,4

REG/NAL@ 7rLoR GeoRef 7/oms BAKER Apxjil 20, 19.37. R. TAYLOR ET Al. 2,077,861

TELEPHONE SYS TEM REG/NMD 7YL0R GeoRef 77-/aM4s BAKER Arrf April 2o, 1937.

R. TAYLOR T AL 2,077,861

TELEPHONE SYSTEM Filed April 23,Y 1934 14 Sheets-Sheet 5 Gamas 7foms BAKE/e Wmumw.

April 20, 1937. R TAYLQR ET AL 2,077,861

TELEPHONE SYSTEM Filed April 23, 1954 14 Sheets-Sheet 6 Arrr;

API'il 20, 1937. R. ATAYLOR ET Al.` 2,077,861

TELEPHONE SYSTEM [NVE/vrees Ffa/NAM 7 no@ Geo/ese X11/oms .BA Ke@ rrr April 20, 1937. R. TAYLOR ET AL TELEPHONE SYSTEM File April 23', 1934 414 Sheets-Sheet 8 [NVE/v Toffs REG/NAL 'aYLoR Gema: Flows BAKER April 20, 1937. R. TAYLOR ET AL 2,077,861

TELEPHONE SYSTEM Filed April 23,' 1954 14 sheets-sheet 9 HNP April 20, 1937. R. TAYLOR ET AL TELEPHONE SYSTEM Filed April 25,1954

14 Sheets-Sheet 10 April 20, 1937. R TAYLOR ET AL' 2,077,861

TELEPHONE SYSTEM Filed April 23, 1934 14 SheetS-Sheerll -f/vve/vrons- REG/NAL@ 7r/.0R 65eme Moms BAKER April 20, 1937. R. TAYLOR ET Al. 07728.61

TELEPHONE SYSTEM Filed April 25, 1934 14 Sheets-Sheet l5 Rea/NMD 7qrLoR Geoeae THOMAS BAKER April 2o, 1937. R, 'TAYLOR ET AL 2,077,861

TELEPHONE SYSTEM v Filed April 25, 1954 14'sheets-sheet 14 A 355 if; i JJ/r4 i aff r .mi H y -NVEA/roms- Rea/NAM 7rLoR G50/Q65 7km/1s BAKER Affr- Patented pr. 20," 1937 UNITED vSTATES man PATENT OFFICE TELEPHONE SYSTEM Reginald-Taylor, Liverpool, England, and George Thomas Baker, Glamorganshire, Wales, assignors to*` Associated `Telephone and Telegraph Company, Chicago; Ill., acorporation of Dela- Application'April-Z'1934, Serial No. 722,012 In Great Britain April 24, 1933 4A Claims.

being used for sendinga'signal over the selected' line'.

According to another feature of the invention, a final selector for use in bothpreferred and non l5 preferred calls is' arrangedv to test the selected line and to transmit back asignal tocontrol a switching operation at a preceding stage when the selected line tests idle, said'signal being the same on both types of call. k According to another feature of thev invention, a telephone system includes secondary finders having access to overow'nders'which haveV access to subscribers lines and are only made available for use when all 'the regular primary finders having access to the same subscribers lines are busy and said secondary finders also have access to junctions incoming from another exchange. According` to a further feature of the invention,

in a telephone system including primary and secondary lnder switches markingpotentialis `arranged to be extended from common control apparatus associated Withthe primary finders to mark a contact in the banks of the secondary finders andholdingpotential is subsequently fed back to the primary nder over the same bank.

The invention will be better understood` from the following description offone` method of carrying it into eifect, reference being had'to the accompanying drawings, Acomprising FiguresY 1 to 14, which should be arranged as shown in Fig. 15.

Fig. 1 shows the trunking diagram of an 800- line R. A. X. (Rural Automatic Exchange). Figs. 2 to 8 show the line finder arrangementusing` the partial secondary. hunting feature, Whichfwas disclosed in United States PatentiNo. 1,914,540, issued June 20th, 1933.

Figs. 9 to 10 Vshow a battery feeding first selector. Figs. 11V and12 show a200line P. B; X. nal 50, selectorarrangedi for toll (or trunk) offering,

while Figs. 13 and 14 show an incoming selector which terminates a junction from the parent ex-r` change and is accessible to both automatic subscribers and operators. It provides trunkoifering facilities-tor the la-tter overthe' regular final'- selectors and has access toadjacent rural exchanges.

Beforedescribing the operation of the circuits, it will be observed from'the trunking diagram (Fig. 1) that the subscribers lines SL are connected over the main frame MDF and the intermediate frame IDF, tothe banks of 10G-point primary line nders designated PF. The subscribers meters are designated SM andthe subscribers line'and cut-off relaysA are designated 10 LC. r

These nders are connected with 10"-leve1, 10- trunk, group selectors designated GS on the basis ofpartial secondary working. This means that the finders PF are divided into twogroups', reg- L5" ular and auxiliary, of which the regular finders RF are connected direct to regular group selectorsY RS, while the auxiliary finders AF are connected over'the 'secondary finders SFto auxiliary group selectors AS located in a common group, and20 accessible to all auxiliary finders in the exchange.

Direct junctions AE from adjacent exchanges, designated 4-8'are connected tol b'othway junction relay'sets BWJ, and appear on' the banks of the secondary finders SF over which they. have" 25' access to the auxiliary rst selectors. This feature is particularly desirable from a traific point of view since it enables'use to be made of group selectors which would otherwise only be used during peak local conditions. 30

The junctions ME fromthe main exchange are similarly connected to bothway junction relay sets BWJ I and are terminatedA on individual in; coming selectors IC, thereby obviating th'enecessity for multi-exchange area' automatic sub- 35 scribers and operators on the main,` exchange Waiting for a second dial tone when calling R; A. X.s of this type.

For local calls the first selectors are digitabsorbing and are provided with a transmission 40 bridge and they are also arranged to pass on discriminating' signals according as the subscribersare ina regular or a coin-box group.

In the drawings, the levels 0, I, 2, and 3 are shown'as having access to four groups of 20D-line 45 nal selectors designated FS, thus giving a local capacity of 800 lines with a more regular numbering scheme than has hitherto been possible, while still leaving levels 4, 5, 6, 1, and 8 available for direct junctions to ve adjacent rural exchanges, thus further simplifying the numbering scheme and permitting alternative routing to be effected in a simple" manner, as will. be' described later.

' 'Ihe'four figure numbers, adjacent'to the banks 5 of the nal selectors FS indicate the respective groups of subscribers served thereby.

It will be appreciated that the local line capacity can, if necessary, be increased to a maximum of 1,800 lines at the expense of one R. A. X. level for each additional 200 lines Outlets from level 9 are connected to the both- Way relay sets BWJ I associated with junctions to the main exchange, and the switch is arranged to cut in on this level if either 9 or 0 is dialled, arrangements being made to prevent the selector stepping to the level exceptwhen the rst digit of a local number (2 or 3). has been previously dialled.

In the case of incoming junctions from the adjacent R. A. X.s which require direct connection with the main exchange, the bothway junction relay set terminating the junction maybe arranged in response to a characteristic signal to set in operation a hunting switch TF shown dotted, to effect the desire throughrconnection.

Referring to Figs. 2 to 8, it should be explained that the nder circuits shown therein employ several of the features of the nder circuits shown in United States specification No. 1,914,540 issued June 20th, 1933. In the arrangement shown in the accompanying drawings, however, the primary nders are D-line switches instead of 200- line switches and have access therefore only to subscribers in their corresponding group.

When a, call is originated in the A group only the start circuit is extended to the control relay sets of both groups of finders, relay ST is operatedin the A group control relay set and relays ST and SR are operated in the B group control relay set. Two nders are thereby taken into use for one call, but during this condition the B group control relay set has access to only A group nders so that the two finders selected are in the A group. The reverse is true for a, call originated in the Bgroup.

If calls are originated simultaneously in both groups each control relay set will then have access to its own group of nders so that one nder only is started in each group.

In the case of a breakdown of one of the control relay sets the other control relay set maintains the service by hunting over either the A group or B group vof finders as determined by the calling circuit.

The number of groups of finders controlled by each relay set may be more than two and the selection of a finder in the proper group may then be controlled by separate start relays.

During partial secondary working, the P wire is used first as a marking wire and subsequently as a guarding and holding wire, so as to free the D wire for use as a metering and discriminating lead.

Considering now the detailed circuit operation, when a subscriber connected to the line circuit shown in Fig. 2 originates a call, relay L is operated over the negative and positive lines in series with the substantial circuit and at armature Z1 marks the calling line in the rotary bank multiple of the finder, and at armature Z2 marks the calling level in the vertical Vbank multiple of the finder. The common start relay S is thus operated in parallel with the vertical bank marking and at armature Sl (Fig. 6) completes a circuit for operating the start relay ST of the A group control set to battery by Way of the low resistance I0. A branch circuit is also completed by way of the metal rectifier ZMRC for operating relay ISR in series with the start relay of the B group disrelayffor each group of finders.

2,077,861 n Y ,Y

tributor and a portion of this circuit is shown enclosed in the dotted rectangle to the left of Fig. 6. It Will be understood that the A and B group line finder distributor circuits are substantially identical with each other and the operation of relay ISR in the B group distributor serves to change over the testing circuit so that this distributor will hunt over the A group of finders only during this condition. Metal rectifiers IMRC and ZMRC are provided to separate the respective start circuits and ensure that the respective SR relays are not operated from their own start circuits. Instead of using the metal rectiers similar results may be obtained by employing a separate start Certain armatures in the distributor circuit are placed in a vcircle to indicate that they belong to a. relay inv A Ythe other distributor.

Considering now the operation of the start relay ST of the A group, it will be seen that at armature stl a battery testing circuit is completed via relay LK for the distributor switch ALD while at armature t2 to std circuits are extended for controlling the operation ofthe time cut-o relays TA and 'IB which will be described later. Due to the operation of armature stl the interrupter relay G operates over its lefthand winding in series with the left-hand winding of relayLK the latter remaining inoperative owing to the high resistance of relay G. Relay G at armature gl (Fig. '7)V completes a circuit for the driving magnet ALM of, the distributor switch in series with the battery feeding relay BP. Relay G therefore interacts with the driving magnet ALM to rotate the wipers of the distributor switch in search of a free finder. It should be explained that all the regular and auxiliary nders of the A group are connected to the test bank la of the distributor switch, the auxiliary finders being normally busied against selection by earth extending from armatures of a relay RFB which is not operated until all the regular finders have been taken into use. The dotted strap in the drawings indicates the direct connection Which is made for regular finders, while in the case of .auxiliary finders the circuit is completed over the armatures rfbd to rfbS of relay RFB and armatures rfzl to 17.24 of relay RFZ when these relays are operated. The test bank 2a of the distributor switch has access when required to all the regular and auxiliary finders in the B group and to prevent the switch from stopping in engagement with one of these nders when testing in the A group over bank la, arrangements are provided to ensure that Whichever test wiper is connected up there is no possibility of it coming to rest in engagement with a nder of the opposite group.

For the purpose of this description it will first be assumed that regular nders are available and therefore, the operation of the secondary finder apparatus shown in Figs. 5 and 8 will not arise at this time.

When the Wiper la comes into engagement with a free regular finder, idle marking battery is picked up over a circuit including the vertical Wiper VW (Fig. 3) in its normal position over an I. D. F. connection shown in Fig. 4 to battery fed via-resistance Il (Fig. 5). This battery connection is suiciently low in resistance to shortcircuit relay G against further operation and relay LK therefore operates over both its windings in series and at armature llc! completes a holding circuit for itself lover its low resistance right-hand winding which is suiiciently low in resistance to guard the regular finder selected from other hunting switches. It will also be realized that during normal conditions and in the absence of a call', relay G may be operated in series with the right-handV winding of relay LK to guarding earth picked up by wiper la. This causes the line finder distributor to perform a preselecting operation although it will be understood that the actual switching through as described, is controlled over the battery testing circuit. The distributor therefore performs a double test on each contact toguard against false switching on to a disconnected finder.

Relay LK at armatures Z762 and llc3 completes holding circuits to relay ST and at armature Zc (Fig. 7) operates relay VR. Relay VR at armature vri operates relayE in thendenat armature W2 operates relay SF in the control circuit from earth. extended from the regular finder over the dotted connection designated REG, at armature UTS operates relay C, and at armature ort provides an alternative locking circuit for relay LK. Relay E in the finder with operating removes earth from the common conductor l2 at armature el (Fig. 3) to indicate the nder as busy to the secondary changeover relays RFB and RFZ (Fig. 7) and at armature e2 prepares a circuit to the Vertical magnet VM. Relay C at armature cl completes a circuit over wiper 6a for relay H in the finder, which at armature h3 completes the circuit to the vertical magnet VM and at armature h3 (Fig. 3) connects direct earth to the testing bank of the distributor to: mark the finder selected as busy. The vertical magnet therefore energizes to raise the shaft and wipers to the-rst level and off-normal springs Nl to N3 are thereby operated; springs NI prepare a circuit to the release magnet ZM and springs N3 prepare a circuit to the rotary magnet RM. At the end of the vertical magnet stroke the interrupter springs om (Fig. 3) close and provided the first level is not the one marked, a circuit is thereby completed over wiper 4a of the distributor for operating the interrupter relay G over its righthand winding. Relay G thereupon at its armature gl (Fig. 7) opens the circuit to the vertical magnet and interaction takes place between the two until the marked level is found, or alternatively, the wipers are raised to the B level. The metal rectifier is connected so as to prevent the operation of relay VT from' battery connected up by the interrupter springs om.

When the marked level is found as indicated by the connection 0f battery to the relevant contact in the vertical bank, relay VT (Fig. 6) in the distributor is operated in a circuit extending over springs NRI (Fig. 3) bank 3a and both its windings in series with relay G which holds to maintain the vertical magnet circuit disconnected. Relay VT then locks over its upper winding which is sullciently low in resistance to mark the vertical level selected as busy to other hunting switches, and at armature @t2 opens the circuit to relay C (Fig. '7). Relay C releases after its slow period and opens the circuit of relay H in the finder at armature cl, while at its resting armature c2 relay RS is then operated and locked over an alternative circuit formed by way of armature rsl. Relay RS at armature rc2 completes an alternative circuit for relay ST (Fig. 6) and at armature TSS (Fig. 6) disconnects relay VT and prepares a circuit to the rotary testing relay PA. Relay H in releasing transfers the impulsing circuit to the rotary magnet RM at armature h3 and also by connecting up earth at armature h1 short-circuits' relay VT in the distributor which releases.

Upon the release of relay VT the rotary magnet RM of the nder is energized to; rotate the wipers into lengagement with the first contactI of the level selected. Normal rotary springs NRt and NR2 operate when the shaft commences its rotary movement; springs NRi extend a ccnnection from relay PA to the test wiper P of the line nder, and springs NRZ close a point in the release trunk conductor to the first group selector associated with this nder. It will be uhderstood that the springs NRE are eifective only in auxiliary finders and in the case of regular finders such as the one in question, they are jy permanently short-circuited oy the dotted strap At the end'of the Vrotary magnet stroke the springs 'rm close and' provided the first Contact does notA connect with the line marked, relay G -f' is again operated. Relay G thereupon inter-acts with the rotary magnet RM to rotate the'wipers into engagement with the calling line. wipers fail to find the calling line they are ro tated to the 11th step position where wiper P il engages contact l is. ,The finder switches through and then restores to normal. When the calling line is found the P wiper encounters battery from the line circuit and relay PA in the control set is operated in series with relay G which :i

holds. Relay PA re-operates relay C (Fig. '2) which locks in parallel with relay RS, at armature c5 short-circuits relay LK (Fig. 6) and at armature cl re-operates relay H (Fig. 4) in the finder. and h2 extends direct earth to the P wiper and this brings abo-ut the operation of relay K in the line circuit in series with relay L which holds. Relay K in the line circuit opens the start circuit to: relay S and clears the battery and earth connections from the calling line which is then extended over the armatures h andlt tc the selector associated with the line nder, for example, that shown in Figs. 9 and l0.

As will be described later, in response tc the .A

switching-through of the calling line, the associated group selector is prepared for the reception of the dialled impulses and it accordingly extends dialling tone over the lower speaking conductor to the calling subscriber, and returns earth potential over the P wire to hold the switching relay H of the nder and the L and K relays in the line circuit. As a result of the short-circuiting of relay LK this relay releases and in turn releases the control set and the wipers ci the distributor switch ALD are then stepped v@nto the next set of contacts. n

Consideration will now be given to the case when all regular finders in the group are in use, so that a further call will have to be completed over one of the auxiliary nders and for this purpose use is made of the secondary equipment shown in Figs. 5 and 8 which performs a hunting operation to associate one of the selectorsv in the common group with the auxiliary finder taken into use. When all the regular inders are taken into use, earth will be disconnected from the common conductor I2 which connects with the resting off-normal springs Nl (Fig. 3) of all the regular nders in the associated group and consequently when the battery feeding relay BP (Fig. 7) again operates as the distributor kicks on at the termination of the previous connection a circuit is completed for energizing relays RFB and RFZ (Fig. 7) in parallel. It will be appreciated that up tothis time these relays have been short- If the Relay H in operating, at armatures hi circuited against operation by the earth on the common conductor I2. Relay RFB at its armature rfbll provides a locking circuit for both relays, and at armatures rfb4, fbS and rfb, rfaI, H22, rfzS and rfzd (Fig. 6) the testing circuit for the distributor is extended through tol the corresponding auxiliary finders. It should be explained that as soon as all regular finders in a primary group become busy, the whole of the group of secondary finders having access to the auxiliary iinders of this particular primary group is opened up, so that secondary distributors such as SDS (Fig. 8) are caused to preselect idle secondary finders such as SCF (Fig. 5) and the manner in which this is effected will now be described.

Relay RFZ in operating, at armature rfz (Fig. 8) connects earth to a common conductor I4, extending to the OB relays of all secondary start groups such as SSI, which for the purpose of this description may be assumed to be two in number. It should be explained that the conductor I4 extends at one end to the OB relays of all secondary start groups and extends at theother end to armatures rfz of al1 primary distributor groups with which the secondary start groups are associated.

Assuming that at least one secondary finder SF is available in the group, relay OB will be operated over the following circuit: earth on common conductor I4, metal rectifier 4MRC winding of relay OB, common conductor I5, resistance I6 (provided one per secondary finder) armatures slc3, sk2 and slcI to battery by way of the resistance Il (also one per secondary finder). Relay OB at armature obl connects earth to a common conductor I8 to short-circuit relay EB which is common tor the whole exchange, and at armature 0h12 operates relay FB. Relay FB at armatures JbI and fbZ removes earth from the leads I9 and 20 which are connected to common terminals on the distributing frame IDF from which connections extend to the auxiliary finders, and replaces this with idle marking battery by way of the windings of relay DS. Relay FB, also. at armature fb3, completes a preselecting circuit for the secondary distributor switch SDS and at armature fb4 completes` a similar preselecting circuit to secondary distributor switch No. 2 previously referred to. Both secondary distributors therefore, hunt to: find a free secondary finder as indicated by the absence of earth on the contacts encountered by wiper 4b. If the secondary distributor switch shown is standing in engagement with a secondary finder which is already in use, wiper 4b will encounter earth from the armature S762 and this operates the interrupter relay GG in series with the upper lowresistance winding of relay DK. Owing to its high resistance, relay GG only operates in this circuit and thereupon interacts with the driving magnet SDM to rotate the wipers into engagement with a free secondary finder as indicated by absence of earth. By this means two idle secondary nders are preselected for use and no further circuit operations take place until another call is originated. When this occurs the subscribers start circuit is again extended to the primary distributor as already explained and the switch ALD thereupon selects an idle auxiliary finder over wiper ICL. Relay LK then operates and the following circuit is completed: earth armature ZlcI, low resistance right-hand winding of relay LK, armatures tb2, 0fb3, s12, wiper and bank Ia, armatures rfb4 and h8, wiper VW, terminal S on the distributing frame, conductor 20, armature ft2, lower winding of relay DS' to'v battery. Relay DS operates and shunts armature fbZ by armature dsZ. At the same time the operation of relay VR (Fig. 7) in the distributor circuit extends a marking battery by way of the high resistance relay SF in parallel with the low resistance 2l over armature W2, wiper and bank la, and over the conductor P to mark the position of the auxiliary primary nder selected in the bank multiple of the secondary finder. Similar operations take place in the other primary distributor. The hunting operation of the two auxiliary finders continues without interruption until the calling line is located, but at this stage the switching through of the finders is suspended since there is no circuit for operating the controlling relays SF until one of the secondary finders locates the corresponding auxiliary finder.

Considering again the operation of the secondary nder equipment, relay DS in operating at armature ds3 completes a switching circuit for relay DK in the secondary control group SCI, and at armature dsa completes a similar circuit for the other control group. As regards the control group SCI it will be seen that relay DK is operated over both its windings in series to battery by way of resistance I'! in the secondary finder and thereupon at armature dlcl provides a holding circuit for itself over its upper winding which is suiclently low in resistance to guard the secondary finder selected. Relay DK moreover at armature dkZ prepares a circuit to -the fast operating test relay DK and at armature dk3 completes a self-interrupting driving circuit to the magnet SCM of the secondary finder from earth at armature flcI. Both secondary finders therefore, hunt at high speed to locate the auxiliary nders, and the fact that their wipers will probably be displaced relatively to each other since they are non-homing switches considerably reduces the finding time.

When the successful auxiliary finder is found, relay FK connected to the successful secondary finder operates .quickly and disconnects the hunting circuit at armature flcl At the same time it removes the short-circuit from relay FR which operates over its comparatively high resistance winding in series with the driving magnet SCM, and then locks independently by way of its armature frI Relay FR also opens a point in the circuit to relay GG at armature fr2 and at armature f3 completes a circuit for operating the switching relay SK in the secondary finder. Relay SK in operating at'armature s1c2 and s1c3 marks the `secondary finder as busy to the distributor equipment, and at armatures slcI, skd, S165 and skS extends the P, negative, positive and D wires from the auxiliary finder to the rst selector. Relay SF in the primary distributor is also operated in series with the left-hand winding of relay SK and brings about the switching through of the auxiliary finder in the manner already explained. The calling subscribers circuit is now extended through to the first selector which accordingly returns dial tone and connects direct earth to the P wire to hold relays K and L in the line circuit, relay H in the primary nder and relay SK in the secondary finder. Relay FK in the secondary distributor circuit is short-circuited and released by this earth and in turn short-circuits relay FR which thereupon releases whereupon the switch SDS immediately preselects the next available secondary nder.

If all the auxiliary nders in the A group become busy, relay OFB in the distributor circuit (Fig. 7) is operated when the last auxiliary nder switches through,.and at armature oylnll opens a point inthe circuit to the start relay ST, at `armature ofbfZ Vtransfers the start earth to conductor 22 leading toan overow meter notshown, and at armature olfb3 transfers the test circuit to wiper 2a which .searches over B group finders. Consequently further calls from the A group of subscribers cannot be completed andare diverted so as to operate the overflow meter. It will be understood however that the distributor equipment of the A group is still responsive to calls originated'in the B group of subscribers, andior this purpose the circuit of the start relay ST is maintained over the armature Ioflrl shownenclosed in a circle, to indicate that it is associated with the OFB relay in the -B distributor. The armature IbpI (Fig. 7) is also associated with the B group distributor and is provided for a similar purpose.

In case all Vsecondary nders become busy there Will be no circuit for operating the OB relays (Fig. 8) and consequently the common relay EB is operated. This relay is provided with a number of armatures similar to armature ebl (Fig. 6) and on operation these disconnect the start battery from the respective primary distributors to prevent them functioning during this condition.

In case for any reason a selected iinder fails to find the calling line within a predetermined period of time the cut-off relays TA and TB (Fig. 6) will function to give an alarm, and busy the faulty nder from further selection. The circuit operations which take place will now be described.

It will be rememberedthat when the start relay ST (Fig. 6) operates, a circuit is completed for starting up the S and Z pulse `cams and the lower winding of relay TA is connected to the Spulse cam. When the S pulse is received relay TA operates and locks over its. upperwinding and connects the upper winding of relay TB to the lead extending to the Z pulse cam. If the nder selected fails to find within a prescribed Vperiod the Z pulse operates relay TB which locks over its lower winding and lights the alarm lamp ALM. rRelay TB also disconnects the hunting circuit of the distributor at armature H12, and at armature tbS connects earth to a common conductor `23 extending to a common alarm circuit not shown. Moreover at armature tb earthV on the wiper 2a in the distributor is connected tothe wiper la to busy the faulty nder, andat armature tbl! (Fig. 7) relay H in the nderis operated to disconnect earth from the common conductor I2 at armature h1 so 'as to mark this finder as busy to the overflow relays RFB and RFZ. These conditions obtain until such time as the fault is cleared, whereupon the attendant releases the equipment by operating the re-setting keyT in the distributor circuit.

Upon the release of `the connection when the calling subscriber replaces his receiver, earth is removed from the release trunk conductor P by the controlling switch in the train, and relay I-l in the primary iinder and relay SK in the secondary finder release as `also do relays K and L conductors,;relay IA operates and at armature Zal in turn operates Vrelay IB and IC in parallel.`

Relay IB at armature Zb-I connects earth to the release trunk conductor P to guard the circuit and hold operated the switching relay in the preceding circuit, and at armature Z192 connects dial tone to the lower speaking conductor to inform the calling subscriber that he may now commencey to dial. Relay IC is operated to prepare the impulsing circuit. ,Y

in the case of calls to the manual board, subscribers dial the digit 0 whereupon relay IA responds` and repeats the impulses through the low resistance winding of relay IC to the Vertical magnet IVM which energizes to raise the shaft and wipers to the desired level. @iT-normal springs 'INI-IN5 are operated when the .shaft leaves its normal position yand are withoutimme` diate effect except'for opening the initial energizing winding of'relay .!IC, vwhich however, remains held during the impulsing yin series vwith the vertical magnet over its lower winding.v Relay IB is similarly held 'during the impulsing period by reason ofthe copper slug surrounding its core. When the shaft and vwipersreach the 9th level the vertical-wiper IVW (Fig. 9) will also come into its 9th position, and Awhen relay I'A again operates at rthe Vend of the 9thV impulse,"re lay IW then operates over the vertical bank Vand armatures Ic6 and Iws3 in series with the Vertical magnet IVM which isinoperative in this circuit. Relay IW at armature IwI disconnects the impulsing circuit Vto the Vertical magnet `so that the 10th impulse is not effectivexas regards raising the shaft and wipersand servesto operate relay IMC which locks. lIt will be appreciated that this'principle 4whereby certain of the impulses control the setting of aswitch andthe re` mainder control adifferent operation is capable of Wider application. If the second portion `oi" the impulse series comprises more than one im.- pulse, they may bev registered by an auxiliary switch` or countingzrelays which may subsequent` ly control the transmission of different signals in accordance with'their setting. Such auxiliary apparatus may be :associated in common with a group of switches.

At the end of the impulsing period relay IA remains held'and relay IC releases after its slow period and releases lrelay IW. A circuit is now completed to the rotary magnet IRM for advancing the wipers into engagement with the rst trunk of the 9th level, and the circuit may be traced from earth at armature Ibl` (Fig. l0)4 armatures Iw4, Imc5, Ig2, Ih3, Icc5, springs IN3, armature Ibll, 4winding of rotary magnet rIRM to battery. Normal-rotary springs INR! and INRZ are operated during the first rotary step but are without .immediate effect. If the rst trunk is engaged the P wiper encounters earth and when the rotary magnet springs lrm close relay IG is then operated over its upperwinding to earth extended lover wiper P and armatures Ih! and IbG. The same earth also short-circuits the switching relay IH to prevent 'it from operating during these conditions. Relay IG at armature Ig2 disconnects the rotary magnet 'circuit and when the rotary magnet springs Irm open, relay IG releases to again complete the'magnet circuitand this action continues automatically until an idleoutlet is found or the wipers reach the 11th position.

When an idle outlet is found as indicated'by the absence lof earth potential on the contact engaged` by the P wiper, the switching relay IH operates in series with relay IG but the latter remains inoperative owing to the high resistance of relay IH. Relay IH at armatures IhI and Ih2 completes a locking circuit for itself in series with the vertical magnet IVM which is also inoperative, at armature Ih3 disconnects the circuit to the rotary magnet IRM, and at armature Ih4 releases relay IMC and operates relay ISW. Relay ISW at armature IswI provides 'a locking circuit for relay IH after the release of relay IMC, at armature Isw2 extends a connection from armature I mcd to the wiper D, and at armatures Isw3 to I swG disconnects the battery feeding bridge in the selector and extends the calling circuit straight through to a relay set (not shown) connecting with a junction to the parent exchange. Relays I a and IB are now released but before the release ofthe latter the relay set returns guarding and holding earth over the P wiper and bank contact to hold the switching relay IH. As explained relay IH also releases relay IMC but the latter owing to its slug remains held for a short period, sufficiently long to extend a signal over the D wiper to the relay set selected,

Y thereby indicating that this call is intended for the manual board. This causes the relay set to extend a manual board calling condition to the parent exchange. When relay I MC eventually releases the D lead is connected straight through to the calling line circuit and in the case of regular subscribers then serves as a metering lead, the metering being controlled from the relay set.

If the called party is a coin'box subscriber, the D lead is connected to a high resistance battery in the line circuit instead of to the meter, so that battery is maintained on the D lead after the release of relay IMC and constitutes a coin box signal to lthe relay set, thereby causing it to extend a different class of signal to the parent exchange to indicate that the call has been originated by a coin box subscriber.

If all the outlets are engaged the Wipers rotate to the 11th step Where cam springs ISI-ISS are the lower speaking conductor to inform the call-' ing subscriber that the connection is unavailable. Subscribers requiring connection with automatic switches in the parent exchange dial the digit 9 whereupon the wipers are stepped to the 9th level, where relay IW operates as in th-e case when the digit 0 is dialled. Since, however, there is no 10th impulse, relay IMC remains normal and when relay IC restores at the end of impulsing the wipers automatically cut in on to the Ilrst outlet. From this point the operations proceed as previously described except that when a free outlet is found and relay IH switches, no signal is connected to the D wiper because of the non-operation. of relay IMC and consequently the relay set selected extends the automatic calling condition to the parent exchange. Single or zone metering is controlled from the relay set over the D lead.

For calls to an adjacent rural exchange, the dialling of the first digit of the prefix raises the Wipers to the desired level and when relay IC restores, the switch hunts for a free outlet in the manner previously described. y u

When a free outlet is found, relay IH switches and extends theA calling circuit tol the associated relay set which provides the transmission bridge and controls metering. If alternative routing is provided, the outlets immediately following those associated with direct junctions are connected to relay sets associated with junctions to the parent exchange, so that in the event of all direct junctions being found busy the selector continues to hunt over the same level to select a junction to the parent exchange. For this purpose a two or three digit prefix is allocated to the adjacent R. A. Xs and arrangements are made for suppressing certain of these digits when a direct junction is selected, whereas if the call is routed via the parent exchange all digits are effective in setting up the required route. In the drawings the vertical bank is shown typically wired so that levels I and 8 serve R. A. Xs in the single fee area and levels 4, 5 and 6 serve R. A. Xs in the excess fee area.

When the switch istaken into use by a coin box subscriber relay ICB is operated over the D lead from the discriminating battery in the line circuit and thereupon locks over its light armature IcbI for the remainder of the connection. It will be assumed that the coin box subscriber dials an excess fee area. When relay IC releases at the end of the digit, relay ICC is operated over the vertical bank and vertical wiper in position 4, 5, or 6 and locks by way of its armature IccI and at armature I ce2 (Fig. 10) operates relay IMC which also locks and completes a circuit for the vertical magnet IVM which may be traced from earth at armature Ih'l (Fig. l0) armatures Iw4 (Fig. 9) Imc5, Ic5, Ig2, Ih3, Icc5, winding of magnet IVM to battery. The vertical magnet therefore energizes to raise the shaft and Wipers to the next level and at the end of the magnet stroke the springs Ivm close and operate relay IG over its upper winding. Relay IG in turn opens the circuit to the vertical magnet IVM at armature Iy2 and interaction takes place between the two until until the wipers are raised to the 9th level.

In this position earth on the vertical bank holds the vertical magnet IVM over a comparatively low resistance 30, and during the holding period relay IW is operated to release relay ICC. Relay ICC releases relay IW and in turn the vertical magnet whereupon the wipers cut in over the 9th level and proceed to select a relay set associated with a junction to the parent exchange. The operation of relay IMC results in a manual callingr condition being extended to the parent exchange together with the coin box signals so that the call is routed to the manual board as described in the case of the dial 0" call.

Local numbers consist of four digits commencing with either 2 or 3, the rst digit serving to prepare the circuit for pre-switching the wipers of the final selector on to the correct hundreds group of lines when it is subsequently taken into use.

If, for example, the digit 3 is dialled the selector steps to the 3rd level Where the normal post springs INPI (Fig. 10) operate and in turn energize relay IW when relay IC releases at the end of the digit, over the following circuit: battery, windingof vertical magnet IVM, winding of relay IW, armatures Iws3 and I c6, springs INPI, armature Ib'I to earth. Relay ICB is also operated over the vertical wiper and bank armatures Icb3, Ic'I, Ib'I. Relay ICB locks up and in conjunction with relay IW completes the following circuit for the release magnet IZM which restores the shaft and wipers to normal: battery, winding of release magnet IZM, armatures Iw5, and Icb3, bank contact and vertical Wiper IVW, armatures IcbI and Ibl 

